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Basic Architecture

Basic Architecture. the main components of a simple computer and their interconnections. The component parts of the computer are:. Processor . Carries out computation and has overall control of the computer. Main memory. Stores programs and data while the computer is running. Is fast

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Basic Architecture

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  1. Basic Architecture the main components of a simple computer and their interconnections.

  2. The component parts of the computer are: Processor. Carries out computation and has overall control of the computer. Main memory.Stores programs and data while the computer is running. Is fast access, directly accessible by the processor, limited in size and non-permanent. External memory.Holds quantities of information too large for storage in main memory. Slower access than main memory, not accessible directly by the processor but can be used to keep a permanent copy of programs and data. Peripheral devices (input/output devices).These allow the computer to communicate with the outside world. External system bus.This allows communication of information between the component parts of the computer.

  3. a schematic diagram of a typical microcomputer system built around the 6502 microprocessor.

  4. The 6502 microprocessor (introduced in about 1975) was among the first microprocessors to be used in early home computers. The 6502 processor included the usual Arithmetic/Logic Unit with some internal registers and a Control Unit all on the same chip. It had an external crystal-controlled clock to generate timing signals. The external bus was a combination of an 8-bit-wide data bus, a 16-bit-wide address bus and some control lines that carried synchronisation signals throughout the system. Hence only 8 bit data could be moved around the system, but 16-bit addresses could be used to address memory. Early models ran at a clock-rate of 1 MHz but some later processors ran at 6 MHz. However with its limitation to an 8-bit-wide data bus and 8-bit arithmetic with no multiply or divide operations, it could not compete with later 16- and 32- bit microprocessors. The Intel 8086 series of processors were introduced in 1978 and were used in the early IBM PC.

  5. The 8086 had the capability to address 1 megabyte of memory since 220 = 1,048,576. the 8086/8088 processors ran at a clock rate of 4.7 MHz and could execute some instructions in as little as 400 nanoseconds compared with the two microseconds of earlier 8-bit personal computers Memory Computers can store data in internal memory (within the computer itself) or external memory (backing storage). Internal memory is any memory device located within the computer system itself. This includes:- Registers (storage within the processor) Cache memory (may be in the processor, or just outside it but on the (motherboard) Main memory (mostly RAM, in separate memory chips on the motherboard)

  6. Registers A typical processor may have hundreds of registers. A few of these have very specific purposes, and have names, including: the memory address register (MAR) the memory data register (MDR) - sometimes called the memory buffer register (MBR) the program counter (PC) the instruction register (IR) The other registers within the processor are called general purpose registers, and can be used by the processor for storing and manipulating any data as required.

  7. registers are part of the processor chip access to the data in them is almost instantaneous, measured in nanoseconds (10-9s) they are limited in number, anything from a few in early microprocessors up to a few thousand in more recent processors they are used to hold data temporarily which is needed immediately by the processor

  8. The main memory consists of individual memory locations, each able to store several bytes (typically 4 or 8 in current systems), and each with its own unique memory address, so that the processor can access any item of data directly.

  9. a typical motherboard layout. The position of the main processor chip, soldered on RAM chips, slots for additional main memory, and cache memory chips.

  10. Typical access time to get data from main memory to the processor would be in the range 10-100 nanoseconds, with data transfer rates of up to 3Gb per second for the latest RAM chips. One solution to this problem would be to increase the number of registers on the microprocessor However, this solution is impractical, leading to over complex and large microprocessor chips. Cache Memory Cache is simply very fast memory chips located on the motherboard very close to the processor. cache memory has access times of 10-50ns, with data transfer rates to the processor of over 10Gb per second.

  11. External Memory • Backing storage is provided by external memory devices. There is a wide range of devices available, and the technology is continually improving. • magnetic discs • optical disc • magnetic tape Magnetic Disc The 1.4 Mb capacity made the floppy disc less and less useful The hard disc, still continues to play an important role as the main backing storage device in most computer systems removable hard disc could be purchased for , much cheaper than RAM. The main disadvantage of hard disc systems is that they are much slower than RAM. Access time could be as much as 10 ms (10,000,000 nanoseconds), and the data transfer rate is typically in the range 30-100Mb per second.

  12. Pupil Task Investigating a Hard Disc specification (20 min) Find out the specification (price and capacity) of a currently available hard disc. If possible, find out its data transfer rate in Mb per second. Calculate the cost per Megabyte. For example: a 400GB costing £200 would give 0.05p per Mb

  13. Optical Disc Optical storage technology has developed rapidly since the early 1990s, and looks likely to replace magnetic technology for many applications. The most common is the CD-ROM. During the mastering of a CD, a reasonably high powered laser is used to burn pits, typically 0.5 microns wide, 0.83 to 3 microns long and 0.15 microns deep, in a spiral, outwards from the centre of the disk. If the spiral was straightened out then the data would stretch for four miles!! Open Scholar booklet at page 15

  14. The CD-R drive operates a laser light at one of 3 different levels. At low levels it detects the presence or absence of pits, while at the highest level it can burn data onto the surface. CD-RW these operate using the highest power of laser to melt a small region of the recording layer. After freezing, the middle power laser is used to warm the surface to a temperature that is less than melting point but high enough to create the highly reflective crystalline form. The highest power is then used to write the data. Capacity CD-ROMs are typically 650 Mbytes in capacity. However, the future use of blue lasers, instead of red laser light, will deliver increased CD-ROM storage capacity.

  15. Speed In a single speed CD reader, data can be read at a rate of 150Kbytes/sec. Multiple speed CD readers, such as 8xCD-ROM or 24xCD-ROM can read data at a rate of 1.2 Mbytes/sec and 3.6 Mbytes/sec respectively. 48xCD-ROMs are available, at data rates of 7.2 Mbytes/sec, they pale in comparison to SCSI hard disk drive rates. Comparing optical discs with hard discs Optical storage has many advantages over magnetic storage, but current devices tend to be limited in capacity and have slower data transfer rates than hard discs. CD-ROM or CD-RW is 700Mb. DVD discs can store up to 4.7 or 9.4Gb, which is much more than a CD (enough to store 133 minutes of video on 1 side), but much less than a large hard disc

  16. Optical storage devices tend to have lower data transfer rates than hard discs, although speeds are increasing all the time. At the time of writing, the fastest CD drives were rated as 52X, which means 52 x 150Kbps, which is 7.8Mbps, significantly slower than hard discs data transfer rates. DVD data transfer rates are quoted as multiples of 1.3Mb per second, so a16X DVD has data transfer rate of 16 x 1.3Mbps, which is 20Mbps. However, this is still slower than hard disc speeds If a CD-RW drive is referred to as 32X16X40X. Then this means:- record data (for the first time) at 32 x 150Kbps rewrite data at 16 x 150Kbps read data (transfer it to the processor) at 40 x 150Kbps.

  17. Pupil task Investigating Optical Storage Devices (30 min) Find out the current cost of a single CD-R, CD-RW, DVD-R and DVD-RAM disc. Express this as a cost per Megabyte. Find out and calculate the data transfer rate of current CD and DVD drives.

  18. Magnetic tape You are probably less familiar with magnetic tape as a backing storage method, as it is mainly used on large commercial systems or on network servers, Type of tapeCapacity Maximum data transfer rate DAT 40Gb 5Mb/s QIC (DC 600 or DC 2000) Up to 2Gb 1.6Mb/s 8mm 14Gb 2Mb/s DLT 70Gb 2Mb/s Mammoth 40Gb 6Mb/s AIT 50Gb 6Mb/s magnetic tape is the cheapest form of data storage, but also has the lowest data transfer rate. Therefore its only benefit it is ideal for making and keeping long term backups of commercial data, or backup copies of network hard drives

  19. Pupil task Collect comparison table of storage devices. NEXT go onto Q6-36 on pages 19 through to 26

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